1. Field of the Invention
The present invention relates to vehicle seats, notably wheel-mounted or crawler-track tractors, public works equipments and machines, or powdered military vehicles of all kinds, and more generally to any vehicle intended for travelling on uneven grounds or off the road and wherein the absence of a suspension system or the inefficiency of the existing suspension system does not provide a sufficient degree of comfort for the driver and/or the user.
2. Description of the Prior Art
Various types of seats intended for vehicles of the above-mentioned types and equipped with suspension systems providing an elastic return action and the damping of the seat oscillation in case of shocks and jolts in a vertical plane, are already known in the art. In a known construction, the seat is connected to a frame structure through linkage means constituting a parallel motion mechanism in which the lower links are rigidly coupled to a rubber ring capable of providing said elastic return action and damping the oscillation. This rubber ring is shear- and torsion stressed, and adapted to damp out both shocks and oscillation due to the inherent rubber hysteresis.
Another known construction comprises two pairs of pivoted arms disposed laterally between the squab-supporting cradle and the seat base, the ends of said arms being adapted to move along horizontal runways or guide-paths provided on said cradle and said base. The four arms or links are identical and form two "X", the upper arms being longer than the lower arms. The suspension member of this seat consists of a transverse torsion bar having one end adjustably anchored and the other end adapted to co-act with a link.
Experience teaches that these arrangements are not capable of fully damping out all shocks and oscillation, notably when the second construction is used, which is relatively complicated and expensive to manufacture. In this second device, moreover, the reaction force of the torsion bar constituting the elastic member is transmitted to only one side of the mechanism, thus causing a certain twist and consequently abnormal kinkings of the various metal components of the suspension system. As a result, more pronounced wear and tear of the pivot means are observed on one side of the seat compared with the opposite side.
In the vehicle seat disclosed in the French patent application No. 76.21065 these inconveniences are avoided by providing a suspension system comprising a central inclined main beam pivoted on the one hand to the base frame and on the other hand to the rear portion of an upper frame supporting the seat squab, said main beam co-acting with a pair of parallel lateral arms pivoted on the one hand to the rear portion of said base frame and on the other hand to the front portion of the seat squab frame. Each lateral arm is rigidly connected intermediate its ends to a transverse shaft trunnioned in said main beam.
Thus, the rigid main beam transmits the reaction torque to the elastic member and the latter tends to counteract the vertical movements of the seat squab frame. The assembly comprising the three beam and arms pivoted according to the above-described arrangement constitutes a rigid system whereby the seat squab frame can perform uniform vertical movements consistent with the suspension beat.
On the other hand, a set of rollers associated with the main beam and the lateral arms is adapted to keep the seat in a plane slightly inclined to the horizontal when the seat squab frame is shaken vertically.
This arrangement is particularly advantageous; yet it cannot eliminate completely parasitic mechanical friction contacts in the suspension system.